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'01. 19: Page 1 r, also with ydroelectric I~n Canyon cr~-f~~t and gation proj- , authoriz~d II , Basin hav~ : mad~ from I~vill~ Basin msas wat~r- esir~d addi- d~r~d larg~ '. In urging ,ther sourc~ ,! Colorado 'd &.~:~ion lsas Ba.,:n.n : Colorado- ~it~d Stat~s Ist~rn slop~ ,to th~ 1948 lrado Riv~r .fin~ US~ of li~w in th~ an int~gral consid~r~d n 1959, an 'nly H>9,064 ;9, a figur~ IUn. CoLOkADO from Deaver', vater to ~ de- . withou.c. some THE COLORADO RiVER No,'ember 1966] hich r~pr~s~nt~d a smaller but still constant incr~ase from 1949, when W d' d" 81,332 acr~-feet wer~ Iv~rt~ . B. Lower Basin I. Physical description. The g~ography of th~ Low~r Basin was described in detail by the Spe- cial Master in Arizona fl. California," and that d~scription is bri~f1y sum- mari2~d her~. Th~ Low~r Basin contains rwo principal str~ams, th~ Colo- rado River itself and th~ Gila Riv~r, which rises in west~rn N~w Mexico and flows west~r1y through Arizona to join th~ main stream near the inter- national boundary. The Low~r Basin is compris~d mainly of basin and range provinc~, a r~gion of lower elevations than the Upp~r Basin and con- taining a series of northwest-trending mountain ranges, with interven- ing valleys and desert. ue Ferry marks th~ political division between the Upper and Lower Basins on the main stream; berween Lee Ferry and Hoover Dam the river passes through very rugged country characterized by deep canyons and ]ittl~ habitabl~ land. Below Hoover Dam intermittent level ar~as suitable for cultivation are ~ncount~red, some of which are in- habited. W~st of the river at the international boundary of the United States and Mexico, but outsid~ the narural drainage basin of the river, lies the Salton Basin, a large sump of 7,500 square miles containing the Salton Sea. Some of the ~arliest irrigation from the lower Colorado is found on both sides of the border in this area. The climate of the Lower Basin is extremely arid, but the soil is rich in many places, and with irrigation the land is ex- tremely productive throughout a long growing season. Surface water sup' plies are supplemented by groundwater in some portions of the basin, espe- cially in Arizona, but the latter source has been subjected in recent years to serious overdraft. Th~ principal part of the water supply of the Low~r Basin is found in th~ main stream of the Colorado and is derived, of course, from the Upper Basin. Tributaries joining the main stream in the Lower Basin make a modest contribution averaging less than half a million acre-feet a year." In many years the Gila contribut~s not a drop to the Colorado. For example, from 1942 to 1950 its inflow amounted to only 400 acre-feet, all of which occurred in the year 1947." Even wh~n the Gila does discharge water into the main stream, the water is not available for use in the United States, since th~ point of confluenc~ is below all existing American works. Presumably 7 -45. 1']. UP'PI.'I\ Cow. 'RTVUI CoMM'N AN'!<I. R'E'P., app. E (1959-1960). 4t6. S~e Report of Lbe Special Master J2-14 (1960), Arizona v. Dliforoia, 373 U.S. 546 (1963) [hereinaftu cited as }.filSt"', R~port]. 47. U.S. DEP'T OF INTERIOR, REpon ON na PACIFIC SOunrwUT WATU PUN nJ-S (Table ,) (1963) (hereinafter ciled as W",TU PUN). 48. Maner's R~port J J:2..